Pressure-induced metallization and phase transitions in GeS$_2$

We have studied the pressure-induced structural and electronic phase transitions of crystalline GeS$_2$ ($P$2$_{1}/c)$ to 50 GPa, using micro-Raman spectroscopy and electrical resistivity measurements in diamond anvil cells. The result shows a steady decrease in resistivity to that a metal at around 40GPa. The visual appearance of GeS$_2$ supports the insulator-metal transition: initially transparent GeS$_2$ becomes opaque and eventually reflective with increasing pressure. The Raman and X-ray diffraction result indicates that the metallization is preceded by a structural phase transition.